The invention pertains to an operation known as napping, which has been commonly practiced for a long time in the textile industry. Its purpose is to make some of the fibers which form a cloth extend outwardly from the face of the cloth by means of repeated brushing on one or both sides of the cloth with suitable prongs, so that a fibrous upstanding layer is formed. The napped product has many applications and may be used industrially, or where a decorative or comfortable cloth is required, and even be used to simulate fine furs.
The above mentioned napping operation, originally carried out manually by scratching the cloth with certain dry vegetable thistles, is now carried out with cylinder napping machines, called simply nappers. These machines have a large horizontal rotating drum, on the circumference of which a plurality of satellite cylinders are located, each cylinder being equipped with prongs of steel wire.
In view of the fact that the structure, the operating principles and handling of these machines are well known for more than a century in the textile industry, they will not be discussed in detail. Those unique characteristics will be the only ones mentioned here, which are considered helpful for a greater understanding and clarification of the invention which is object of the present application.
In most napping operations, the object is to form upon the cloth a soft, thick outer layer of the fibers. A typical example of this is found in the manufacture of blankets. In order to obtain such a result, it has been necessary to submit the cloth to an intense napping, which can only be achieved from accumulation, by repeatedly passing the cloth through the machine. The effect can be improved considerably if, after each passing of the cloth through the machine, the direction in which a piece of cloth is passed through the machine is reversed, so that what was once the head of the piece becomes the tail thereof for the next passing step and vice versa, and the strip of cloth--the source of the fibers to be extracted--receives the attack of the prongs from opposite directions, alternately.
This technique is imposed by the nature of the napping machine with cylinders and has been supported by many years in practice. It, however, involves certain limitations and inconveniences which until now have been accepted as inevitable. For example, the repetition of the passing of the cloth through the machine turns out to be expensive in time, energy and labour. Also, the increase in the napping effect due to the repetition of passages has a limit, for each new passage makes it more difficult for the prongs to penetrate the raised layer of fibers generated from the preceding passage, namely fibers which are now flattened by the intermediary piles of cloth. The prongs scarcely manage to extract new fibers from the strip of cloth which remains at the bottom of the layer, but each time they tear out and remove the layer instead of enriching it. When the cloth is to be napped on both sides, these inconveniences are repeated on the second side and experience shows that generally the finishing of the second side is different from that of the first one.
It should be noted that it is not always advisable to decrease the number of passages by means of increasing the number of napping cylinders, since there are certain known physical and mechanical limitations which prevent it and the practice has shown the inefficiency of such a solution. The energy of the napping cylinders in the machine cannot be increased beyond what the resistance of the cloth being processed will permit. And it should also be pointed out in this sense that the resistance of the cloth is not only tested by the napping cylinders, but also mainly when it is removed from the drum at the end of the passage. At this point, the cloth, which bears some very small difference in speeds with regard to the prongs of the satellite cylinders, is subjected brusquely to a difference of speeds with regard to the drum. In addition, the cloth is usually removed perpendicularly of the drum and sometimes in a direction opposite to that of the rotation of the napping drum.